The intima is a normal part of the human artery wall but it is also the soil in which atherosclerosis occurs. Surprisingly, little is known about the intima. .What-we do know about the intima is that one form of it, the fibrous cap of the atherosclerotic lesion -is clonal. Clonality is an unusual feature of tissues other than neoplasms. To study the origins of this tissue, we will use autopsy specimens taken from infant-coronary arteries: This site develops an intima rapidly after birth but later becomes the monoclonal plaque. This tissue, as well tissue from surgical specimens of the intima from arteries in adult humans will be characterized in terms of the identities of intimal cells, using in situ hybridization and immunocytochemistry and in terms of clonal origins using an x-linked CAG polymorphism. Array display of cultured cells, free of local environmental influences, will be used to determine whether plaque clonal cells are like other smooth muscle cells or if, like clonal cancer cells, the plaque cell represents a mutant type. As a more experimental approach to this question we will develop a transgenic mouse model in which clonality can be directly observed. This will take advantage of the existence of mice with a green fluorescent protein gene inserted into the X chromosome. Since female animals have 2 X chromosomes but randomly inactivate one of these in each cell, tissue of heterozygotic female mice can be directly observed by fluorescence confocal microscopy to ascertain clonal patterns. We will cross these mice with mice engineered to have atherosclerosis and determine whether mice, like humans, develop clonal atherosclerotic plaques. Finally, in collaboration with Dr. Bowen-Pope, we will combine these animals with mice using a "lineage trap", a fixed marker that identifies the cell types giving rise to other cells. This will permit us to identify the cellular source of the fibrous cap. [unreadable] [unreadable]